The present invention relates generally to the field of dredging, and more particularly to a dredging system and method of dredging material to a selected depth and depositing the material at an adjacent location such as a beach.
Erosion of beaches is a serious problem and is being addressed by every coastal state in the United States and in coastal areas across the world. For example, the state of Texas currently has a fund of $15,000,000 to renourish or reclaim beaches. Florida has a $100,000,000 annual budget for reclaiming beaches. While these budgets might seem excessive, they are necessary under the current technology to renourish eroded beaches. Currently, it is common to renourish a beach once every ten years or so. In reality, the current process consists of remediating the beach after it has eroded which requires the deposit of much greater volumes of beach quality sand, thus requiring the searching for, and locating of the large sand deposits necessary for dredging at great expense.
To renourish beaches, it is necessary to locate and obtain beach quality sand and deposit it in the desired location. Typically, a sufficient deposit of beach quality sand is found in the gulfs, bays, channels and oceans and is dredged. With the conventional manner of dredging it is required to locate large sand deposits (borrow sites). It is becoming more difficult to locate sufficient sand deposits for conventional dredging methods and systems. Additionally, these borrow sites are being located farther from shore than in the past increasing the expense of the operation.
The dredging of the bottoms of bodies of water usually takes one of two forms, suction dredging or shovel dredging. These conventional methods of dredging are not economically efficient for dredging sand for beach reclamation or nourishment.
In suction dredging operations, a typical system consists of a barge floating upon the water surface and the inlet of a pump suction system positioned below the barge permitting the pumping, and removal, of a slurry formed by the bottom materials and water. A power-driven cutterhead is typically utilized proximate the suction conduit inlet to cut and loosen the bottom material and conveying the loosened material toward the suction conduit. The material is then typically pumped through a conduit to the barge, an adjacent vessel or to a remote site.
Prior art suction dredging operations are inefficient and expensive when utilized for beach reclamation. Typically, the dredging system must be transported to a remote location where a substantial depth of a sand deposit is located. It is not uncommon for fees in the range of $500,000 to $1,000,000 to be charged just for the system to be mobilized and moved to a borrow sight having a large sand deposit. As the sand is dredged it is often necessary to transport the sand via a pipeline several miles to a site for clean up and transfer to trucks for transport to the beach or other desired site for deposit. These remote borrow sites commonly require several vessels for operation, expensive booster pumps to transport the dredged material to a site, and additional vessels carrying pipe for forming a conduit from the remote site to a deposit site. The equipment and logistics of these operations undesirably limit the process to being utilized only when necessary and not as a method of maintaining a beach.
In shovel dredging systems, buckets are manipulated away from or toward an operator to scoop the bottom material into the bucket. The bucket is then raised above the water level and deposited in an adjacent vessel or ashore. Again, this method requires a large deposit of sand having a substantial thickness for the operation to be effective. Shovel dredging also requires the use of several vessels and excessive expenses for transporting the dredged material from the borrow site to a deposit site. Additionally, shovel dredging is inefficient for dredging beach quality sand due to the tendency of the dredged sand to wash from the shovel. It is thus desired to provide a dredging system that is substantially self-contained for dredging material proximate a deposit site. It is a further benefit to provide a dredging system adapted for dredging a bottom material that may have a narrow depth. It is a still further benefit to provide a dredging system that leaves a borrow site substantially environmentally intact, minimizes the effect on the marine life and allows quick, natural repair of the borrow site. It is an additional benefit to provide a dredging system and method provides an economical means of maintaining a deposit site as opposed to remediating or reforming a deposit site.
It is thus one feature of the present invention to provide a substantially self-contained dredging and transport system for mobility reducing the cost of the dredging and deposit operation.
It is a further feature of the present invention to provide a dredging system capable of obtaining quality material for dredging proximate a deposit site.
It is a still further feature of the present invention to provide a dredging system that reduces the detrimental effects on marine life at the borrow site.
It is a still further feature of the present invention allows for relatively quick and natural repair of the borrow site.
Accordingly, a system and method of the type for quickly mobilizing a unit for dredging a layer of material from a water bottom is provided. The dredging system includes: a motorized, substantially self-contained vessel positioned above a borrow site, at least one dredging shoe extended from the vessel to a bottom of a water adapted for dredging a material from said bottom to a pre-selected depth, a power source positioned on the vessel in operational connection with the dredging shoe for drawing the material into the shoe and transporting the material through a conduit to a deposit site, and a dredging motivation system connected to the vessel for moving the vessel and the dredging shoe along a dredging path.
It is desirable to employ a vessel, such as a barge, capable of containing substantially all of the elements of the system for quick deployment. For example, the barge having a sufficient quantity of conduit to be connected or unspooled to connect the dredge shoes to the power supply and form a transport line to the deposit site.
One of the benefits of the system is the ability to dredge material which may not be have a thick enough layer for dredging utilizing prior art methods. For example, beach quality sand is often located within several thousand feet of a shoreline, but often is in a layer of approximately six inches. The current system desirably uses a wheel arrangement and tongue to xe2x80x9cscoopxe2x80x9d a thin layer of material into the shoe. The material is then suctioned by a dredge pump and transported to the beach via the transport conduit. An additional benefit of taking a thin layer of material is the reduction of stirring up mud and silt at the dredging site, thereby reducing the environmental impact of the operation.
The vessel may be navigated along a precise path through the dredging site utilizing a novel motivation system. The system desirably includes a four-point anchor system. An anchor connected by cable is extended from each corner of the vessel and anchored outside of the area to be dredged. Each cable is connected to a winch so that extending and retracting various cables moves the vessel along a selected path. A global positioning system may be controllably connected to the winches to navigate the vessel along the selected path. This method of moving the vessel adapts the system for operations in rough seas. The motivation may include separate motor systems or a motor system in connection with the four-point anchor system.
The dredge shoes may be utilized singularly or in varying combinations. For example, two or more dredge shoes may be connected directly together to create a greater dredge path. Several dredge shoes may be connected with spacing devices, such as bars, to leave on dredged areas between the dredge paths. This manner of dredging reduces the impact on marine life in the area and facilitates quicker recovery of the borrow site and the marine life. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims appended hereto.